1. Field of the Invention
The present invention relates to a light distribution characteristic measurement apparatus and a light distribution characteristic measurement method for measuring the light distribution characteristic of a light source.
2. Description of the Background Art
The light distribution characteristic is known as one of the characteristics of light emitted from a light source. The light distribution characteristic means a spatial distribution of the luminous intensity (or luminance) of a light source. As such a light distribution characteristic, both the absolute-value-based light distribution and the relative-value-based light distribution are used. The absolute-value-based light distribution is a measurement of the spatial distribution of the absolute value of the luminous intensity and is used in such a case where the total luminous flux generated by a light source is to be determined. In contrast, the relative-value-based light distribution is a measurement of the spatial distribution of the relative value of the luminous intensity, and is used in such a case where the light distribution pattern is to be determined. Generally, it is not easy to measure the light distribution characteristic of light sources such as a light source having a complicated light distribution pattern and a light source whose characteristics are not known. Regarding the method and apparatus for measuring such light distribution characteristics, the following related arts are known.
Japanese Patent Laying-Open No. 62-250325 discloses a light distribution measurement apparatus based on a system in which an object to be measured is fixed, a mirror is revolved around the object, and the light reflected from the mirror is measured with an optical receiver.
Japanese Patent Laying-Open No. 2003-247888 discloses a light distribution measurement device including a first rotating stage which is rotatable about a first rotational axis, a second rotating stage which is rotatable about a second rotational axis orthogonal to the first rotational axis and held on the first rotational stage in such a manner that the second rotating stage is spaced from the first rotational axis, and a light source provided so that the center of its light emission surface is located at the intersection of the first and second rotational axes.
Japanese Patent Laying-Open No. 09-203691 discloses a method for measuring a light distribution pattern or the like. Specifically, a light receiving unit in which a plurality of optical receivers are arranged linearly at predetermined intervals is moved in front of a source of irradiation and along the direction orthogonal to the direction along which the optical receivers are arranged, to thereby measure the light distribution pattern.
Japanese Patent Laying-Open No. 2001-174251 discloses a measurement apparatus including a first unit enabling an object-to-be-measured to perform a vertical linear operation and a horizontal rotational operation, and a second unit causing a measurement device to perform a horizontal linear operation, a vertical linear operation, and a revolving operation revolving on a plane defined by these two directions.
Possible light sources whose light distribution characteristic is to be measured range from a small lamp like mini light bulb to a large lamp like vehicle's headlight. In the case where the light distribution characteristic of a light source having a relatively large light emission surface is to be measured, it is necessary that the distance between a detecting unit and the light source (measurement distance) be sufficiently long for the detecting unit to have its field of view which is large enough to encompass the whole light source therein. The above-described related arts have confronted a problem of increased complexity and increased size of an apparatus in the case where the apparatus is designed to measure the light distribution characteristic of a light source whose light emission surface is relatively large.